1. Field of the Invention
This invention relates to a network protector having a cable trip assembly and an electrical close assembly, more specifically, to a network protector which incorporates an interface linkage assembly structured to operate both the cable trip assembly and the electrical close assembly.
2. Background Information
Secondary power distribution networks consist of interlaced grids which are supplied by two or more sources of power so that the loss of a single source of power will not result in an interruption of service. Such networks provide the highest level of reliability possible with conventional power distribution and are normally used to supply high-density load areas such as a section of a city, a large building, or an industrial site. Between the power sources and the network is a transformer and a network protector. The network protector consists of a circuit breaker and a control relay. The circuit breaker includes at least one set of main contacts that move between an open position and a closed position. When the main contacts are closed, electricity may flow through the network protector. The control relay senses the transformer and network voltages and line currents and executes algorithms to initiate breaker tripping or closing action. Trip determination is based on detecting an overcurrent condition or reverse power flow, that is, power flow from the network to the energy source.
Network protectors are often found in dust-proof or moisture-proof housings, or vaults, which are disposed in subterranean passageways in large metropolitan areas. Given their urban, subterranean location, increasing the size of the vault to accommodate larger network protectors is costly and difficult. As such, it is more efficient to reduce the space occupied by certain network protector components so as to allow space for other newer/larger components. That is, by reducing the size of one component or sub-component, another component may be added or an existing component's size may be increased.
The network protector components, the circuit breaker and the relay, are located within a housing assembly within the vault. For safety, the circuit breaker should be tripped before the circuit breaker can be removed from the enclosure. To accomplish this, network protectors include a mechanical trip assembly which is structured to interact with the network protector trip bar. The trip bar is structured to move between a first position and a second position. In the first position, the trip bar prevents the main contacts of the network protector circuit breaker from moving into the closed position. Thus, when the trip bar is in the first position, the contacts are open. In the second position, the trip bar allows the main contacts to be moved into the closed position.
To safely remove, or install, the circuit breaker from the enclosure, the main contacts must be in the first, open position. To trip the circuit breaker, the trip bar must be moved into the first position. A typical mechanical trip assembly is structured to be actuated prior to opening the door to the enclosure. Accordingly, the mechanical trip included an external handle that may be actuated prior to opening the door to the housing assembly. Actuating the external operating handle moves the mechanical trip assembly, and therefore the trip bar, into the first position. Thus, before the housing assembly is opened, the circuit breaker was tripped. If required, however, it was possible to open the housing assembly with the trip bar in the second position, leaving the circuit breaker in the closed position. After maintenance and/or repairs are performed on the circuit breaker or the relay, and after the circuit breaker is installed in the vault, the mechanical trip assembly, and therefore the trip bar, are moved into the second position so that the main contacts could again be closed.
The mechanical trip assembly includes an external handle coupled to a shaft, a lever mounted on the shaft within the housing and a coupling device, such as a cable, extending between the lever and the trip bar. When the shaft is rotated, the lever moves causing the coupling device to act upon the trip bar. Typically, the shaft is structured to move through a lesser arc. That is, the shaft typically cannot move through a greater arc, e.g. greater than ninety degrees, as that amount of rotation may cause the coupling device to wrap around the shaft. The mechanical trip assembly and the circuit breaker are both mounted on a frame that is structured to move in and out of the enclosure. A spring biases the mechanical trip assembly to the first position in which the trip bar was moved into the trip bar first position which tripped the circuit breaker.
In operation, when the circuit breaker was in use and disposed within the enclosure, the lever was held so that the mechanical trip assembly was in a second position holding the trip bar in the second position. Prior to opening the door to the enclosure, a user actuated an external handle which was coupled to the lever, thereby moving the mechanical trip assembly into the first position which, in turn, moved the trip bar into the first position causing the circuit breaker to trip. At this point the circuit breaker could be safely removed from the enclosure. After the circuit breaker was returned to the housing assembly and the housing assembly closed, the procedure for closing the circuit breaker contacts included a step which returned the lever to its original position, i.e., the mechanical trip assembly and the trip bar were both moved into their respective second positions thereby allowing the contacts to be closed.
Newer network protector circuit breakers are further structured to close into electrical fault conditions. The closure of the circuit breaker contacts is accomplished by a closure device having a spring loaded mechanism. The closure device is actuated by an electrical close assembly. The electrical close assembly is, in turn, actuated by a shaft which the user rotates via an external handle. The typical electrical close assembly requires the actuating shaft to rotate through an extended arc.
Presently, newer network protectors with the electrical close assembly are being installed in enclosures structured to be used with older network protector circuit breakers, That is, the newer network protectors with the electrical close assembly are being installed in enclosures that are not adapted to interface with the electrical close assembly. Attempts have been made to adapt the enclosures to accommodate the electrical close assembly. These measures, however, require modification to the housing assembly which are expensive.
It is desirable to have the electrical close assembly actuated by the same external handle as the mechanical trip mechanism. One problem, however, with using a single handle and shaft to actuate both the mechanical trip mechanism and the electrical close assembly is that the mechanical trip mechanism can only move through a lesser arc whereas the electrical close assembly requires the shaft to move through a greater arc.
There is, therefore, a need for an interface linkage assembly structured to be coupled to a shaft on an external handle and to actuate an electrical close assembly and a mechanical trip mechanism.
There is a further need for such an interface linkage assembly to be incorporated into existing network protector and enclosures.